olymmath

HK-PC 2023

Hong Kong Preliminary Selection Contest and TST 2023.

Other problems

Problem 5

Let ABCDABCD be a convex quadrilateral with AB=5AB=5 , AD=17AD=17 , and CD=6CD=6 . If the angle bisector of ∠BAD\angle{BAD} and ∠ADC\angle{ADC} intersect at the midpoint of BCBC , find the area of ABCDABCD .

Problem 6

(a) Find the smallest number of lines drawn on the plane so that they produce exactly 2022 points of intersection. (Note: For 1 point of intersection, the minimum is 2; for 2 points, minimum is 3; for 3 points, minimum is 3; for 4 points, minimum is 4; for 5 points, the minimum is 4, etc.) (b) What happens if the lines produce exactly 2023 intersections?